The invention relates to a refiner for refining fibrous material, the refiner comprising at least one first refining surface and at least one second refining surface, which are arranged at least partly substantially opposite to one another in such a manner that a refiner chamber, to which material to be defibrated is arranged to be fed, is formed between them, and at least either the first refining surface or the second refining surface is arranged to move with respect to the opposite refining surface, and the first refining surface and the second refining surface comprise blade bars and blade grooves between the bars.
The invention further relates to a method for refining fibrous material, the method comprising refining fibrous material with a refiner which comprises at least one first refining surface and at least one second refining surface which are arranged at least partly substantially opposite to one another in such a manner that a refiner chamber, to which material to be defibrated is fed, is formed between them, and in which at least either the first refining surface or the second refining surface is arranged to move with respect to the opposite refining surface, and in which the first refining surface and the second refining surface comprise blade bars and blade grooves between the bars.
The invention further relates to a blade segment for a refiner intended for refining fibrous material, the blade segment comprising a refining surface with blade bars and blade grooves between the bars.
Refiners for treating fibrous material typically comprise two, possibly even more, refining surfaces substantially opposite to one another, between which there is a refiner chamber to which fibrous material to be refined is fed. At least one of the refining surfaces is arranged to move relative to the opposite refining surface. The refining surface may be formed of one integral structure, or it may be formed of a plurality of refining surface segments arranged adjacent to one another, whereby the refining surfaces of individual refining surface segments form one uniform refining surface. The refining surfaces may also comprise specific blade bars, i.e., bars, and blade grooves, i.e., grooves, between the bars, whereby fibrous material is refined between the blade bars of opposite refining surfaces and both the material to be refined and the already refined material are able to move on the refining surface in the blade grooves between the blade bars. On the other hand, the refining surface may comprise protrusions and recesses between the protrusions. The blade bars and blade grooves of the refining surfaces or the protrusions and recesses of the refining surfaces may be made of the basic material of the refining surface or a different material. The protrusions may also be formed of ceramic grits attached to the refining surface by previously known methods. The refining surfaces, i.e., the blade surfaces, may also be formed of separate lamellas arranged adjacent to one another or at a distance from one another and fixed to form a refining surface. The refining surface may also comprise a very large number of small protrusions and recesses between them, in which case the refiner operates by a grinding principle.
The refiner chamber is a volume which is formed between the refining surfaces of a stator and rotor and where refining takes place. The refining is carried out by mutual pressing and motion of the refining surfaces under frictional forces between the refining surfaces and the material being refined and, on the other hand, under frictional forces created inside the material being refined. The surface area formed by the refining surfaces of the rotor and stator between them is the refining area, in which the refining between the refining surfaces of the rotor and stator takes place in the refiner chamber. The shortest distance between the refining surfaces of the rotor and stator in the region of the refining area is the blade gap.
To boost the production of refiners, it is important to be able to guide the fibrous material to be refined efficiently between the opposite refining surfaces for refining. At the same time, it is naturally important to be able to remove the already sufficiently refined material from between the refining surfaces in such a manner that the already refined material does not block up the refiner chamber between the refining surfaces and thus weaken the production of the refiner. Particularly in refining surfaces comprising blade bars and blade grooves between the bars, the guiding of fibrous material between the opposite blade bars has been made more efficient by providing at the bottom of the grooves special dams that force the material being refined to move away from the bottom of the grooves and on between the opposite refining surfaces. However, the effect of the dams is local and thus does not substantially benefit the whole area of the refining surface. The dams also considerably diminish the hydraulic capacity of the refining surface.
By changing the height of the blade groove bottom and/or the volume of the blade groove, it is also possible to try to force the flow of the material being refined to move between the opposite refining surfaces and thus make the refining more efficient. In addition, by tilting the blade bars, it is also possible to try to affect the flow of material being refined and thus force the material being refined to pass between the opposite blade bars.
A problem with all these solutions is, however, that they do not significantly improve the guiding of the material being refined into the refiner chamber without simultaneously weakening the production capacity of the refiner.